In a wireless system, the wireless terminal has a Subscriber Identity Module (SIM), which contains the identity of the subscriber. One of the primary functions of the wireless terminal with its SIM in conjunction with the wireless network system is to authenticate the validity of the wireless terminal (for example, a cell phone) and the wireless terminal's subscription to the network. The SIM is typically a microchip that is located on a plastic card, a SIM card, which is approximately 1 cm square. The SIM card is then placed in a slot of the wireless terminal to establish the unique identity of the subscriber to the network. In some cases, the wireless terminal itself contains the subscriber identification and authentication functionality so that a separate SIM and/or SIM card is not utilized.
In the SIM (or within the wireless terminal) an authentication key and a subscriber identification pair are stored. An example of such a pair would be the authentication key Ki as used in GSM networks and the associated subscriber identification IMSI (International Mobile Subscriber Identity). Another example would be the authentication key A-Key and subscriber identification MIN (Mobile Identification Number) as used in CDMA and TDMA networks. In either case, a corresponding identical set of an authentication key and a subscriber identification are stored in the network. In the SIM (or in the wireless terminal) and within the network, the authentication functionality is run using the local authentication key and some authentication data which is exchanged between the SIM and the network. If the outcomes of running the authentication functionality in the SIM and in the network leads to the same result, then the SIM/wireless terminal are considered to be authenticated for the wireless network.
In existing wireless systems, a SIM (or wireless terminal) has an authentication key associated with only one subscriber identification and this subscriber identity is typically tied to a local region or network. When a SIM (or wireless terminal) authenticates in a region that is not local or with a network that is not local, then usually the SIM (or wireless terminal) needs to pay additional roaming service charges to connect with the wireless network. It would be beneficial if the SIM (or wireless terminal) were not permanently tied to a local region or network. For example, equipment vendors would then be able to sell the same equipment in multiple regions and for multiple networks with one physical SIM card. Additionally, end users may avoid roaming service charges or at least more favorable subscription terms may be available.